Synergy of Light‐Atom Electron Donating and Macroporous Interface Reconstruction Enables Low Iridium PEM Water Electrolysis at High Current Density

Low‑iridium proton exchange membrane (PEM) water electrolysis at high current densities faces two critical bottlenecks, namely impaired electron transport within the catalyst layer due to sparse active sites, and severe bubble‑induced mass transport resistance. Here we break this deadlock via a cross‑scale synergy strategy combining a light‑atom electron‑donating effect with macroporous framework interface reconstruction. Introducing trace nitrogen into a three‑dimensional macroporous TiO 2 lattice significantly narrows the band gap, enhances conductivity, lowers oxygen vacancy formation energy, and strengthens interfacial charge transfer to IrO x , thereby overcoming the electronic isolation issue (i.e., the “island effect”). Meanwhile, the macroporous framework together with nitrogen‑enhanced hydrophilicity reconstructs the gas‑liquid interface, enabling rapid vertical bubble detachment as confirmed by volume of fluid (VOF) simulations. IrO x /N‑TiO x catalyst achieves a mass activity of 472.57 A g −1 , about 31 times that of commercial IrO 2 . Benefiting from excellent mass transfer and catalytic activity, a single cell with an ultralow Ir loading of only 0.19 mg cm −2 requires just 2.086 V at 8 A cm −2 and operates stably for over 230 h at 1 A cm −2 . This cross‑scale synergy offers a powerful route to low‑iridium, high‑current‑density PEMWE.